Viable dual motor/shaft cannot be that far away!
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Direct driven set-up may not work at the weight we want. In-line motors driving independent but coaxial shafts may need to be sized according to the torque requirements of each prop. If one were to gear the shafts down, then one would have little to no difference over the current contra.

A twin motor driving independent and coaxial shafts without an add-on contar drive needs thought and innovation. I don't think it's a straight forward undertaking to create an elegant solution!